The present invention relates generally to the field of electrical circuit breakers, and more particularly to a latch mechanism for a circuit breaker.
In general the function of a circuit breaker is to electrically engage and disengage a selected circuit from an electrical power supply. This function occurs by engaging and disengaging a pair of operating contacts for each phase of the circuit breaker. The circuit breaker provides protection against persistent overcurrent conditions and against the very high currents produced by short circuits. Typically, one of each pair of the operating contacts are supported by a pivoting contact arm while the other operating contact is substantially stationary. The contact arm is pivoted by an operating mechanism such that the movable contact supported by the contact arm can be engaged and disengaged from the stationary contact.
There are several ways by which the operating mechanism for the circuit breaker can disengage the operating contacts: the circuit breaker operating handle can be used to activate the operating mechanism; or a tripping mechanism, responsive to unacceptable levels of current carried by the circuit breaker, can be used to activate the operating mechanism; or auxiliary devices can be used to trip the circuit breaker thereby move the movable contact. For many circuit breakers, the operating handle is coupled to the operating mechanism such that when the tripping mechanism activates the operating mechanism to separate the contacts, the operating handle moves to a fault or tripped position.
To engage the operating contacts of the circuit breaker, the circuit breaker operating handle is used to activate the operating mechanism such that the movable contact(s) engage the stationary contact(s). A motor coupled to the circuit breaker operating handle can also be used to engage or disengage the operating contacts. The motor can be remotely operated.
A typical industrial circuit breaker will have a continuous current rating ranging from as low as 15 amps to as high as several thousand amps. The tripping mechanism for the breaker usually consists of a thermal overload release and a magnetic short circuit release. The thermal overload release operates by means of a bimetallic element, in which current flowing through the conducting path of a circuit breaker generates heat in the bi-metal element, which causes the bi-metal to deflect and trip the breaker. The heat generated in the bi-metal is a function of the amount of current flowing through the bi-metal as well as for the period of time that that current is flowing. For a given range of current ratings, the bi-metal cross- section and related elements are specifically selected for such current range resulting in a number of different circuit breakers for each current range. The tripping mechanism may be housed in the same housing as the operating mechanism and contacts or it may be housed in a separate housing coupled to the housing containing the operating mechanism and contacts.
In prior art circuit breakers, in order to test the operating mechanism of the circuit breaker, it was necessary to place the circuit breaker in an electrical circuit and test it in its overload conditions, since the trip mechanism activated the operating system. Such procedures were time consuming, and placed an unnecessary duty cycle burden on the components of the circuit breaker.
Prior art circuit breakers also can be associated with auxiliary devices such as an undervoltage relay, indicator switches, shunt trip device, an auto trip interlock capability and a test button capability and the like. Prior art circuit breakers typically were designed to have a specific auxiliary device associated with that circuit breaker and either mechanically or electrically coupled to the operating mechanism. Such arrangements required specially designed auxiliary devices for each rating of a given circuit breaker frame and did not facilitate interchange of auxiliary devices with other circuit breaker ratings.
Thus, there is a need for an apparatus for operating a circuit breaker during conditions other than an overload condition. There is also a need for an apparatus for operating a circuit breaker that will disengage the latching mechanism and cause the movable contact to move. There is also a need for a molded case circuit breaker that provides the ability to test and inspect the operation of the operating mechanism independent of a trip unit. Thus there is a need for a latch mechanism that has several features that allow the introduction of accessory devices to interact directly with the operating mechanism of different rated circuit breakers.
The present invention provides an apparatus for operating a circuit breaker. The circuit breaker includes a housing, a cradle mounted in the housing and coupled to a handle and to a movable contact. The apparatus comprises a latch frame mounted in the circuit breaker housing. A latch roller is mounted on the cradle. A latch member is configured to selectively engage the latch roller and the latch member is rotatably coupled to the latch frame. A latch shaft assembly is rotatably mounted in the latch frame and selectively engaged by the latch member. Upon rotation of the latch shaft assembly, the latch shaft assembly will disengage from the latch member and cause the movable contact to move. In one embodiment, a single latch spring is coupled to the latch shaft and the latch member. Another embodiment includes a kicker member mounted in a trip unit. The kicker member is configured to act upon a trip arm and to be moved to a reset position by the handle of the circuit breaker.
There is also provided an apparatus for operating a circuit breaker. The circuit breaker includes a housing, a cradle mounted in the housing and coupled to a handle and to a movable contact. The apparatus comprises a means for supporting mounted in the circuit breaker housing. A means for rolling is mounted in the cradle. A means for latching is configured to selectively engage the means for rolling and is rotatably coupled to the means for supporting. A means for rotating is rotatably mounted in the means for supporting. The rotation of the means for rotating will disengage the means from rotating from the means for latching and cause the movable contact to move.
There is further provided a molded case circuit breaker comprising a housing, an operating mechanism mounted in the housing. The operating mechanism has a cradle coupled to a handle and to a movable contact. An apparatus for operating the circuit breaker during a condition other than an overload condition is also included. The apparatus comprises a latch frame mounted in the circuit breaker housing. A latch roller mounted in the cradle. A latch member is configured to selectively engage the latch roller and is rotatably coupled to the latch frame. A latch shaft assembly is rotatably mounted in the latch frame and selectively engaged with the latch member. The rotation of the latch shaft assembly will disengage the latch shaft assembly from the latch member and cause the movable contact to move.